1. Field of the Invention
The present invention is related to a detector of grass-bag fullness for a mower, and particularly to a detector of grass-bag fullness for a mower which can accurately detect fullness independently of the properties (dry or wet, length, thickness, etc.) of the grass being mown.
2. Description of the Prior Art
A mower for lawn, weeds and the like (hereinafter referred to as grass) has a cutter blade for cutting grass on the underside of it. The mown grass is conveyed within a duct-like shooter by an air flow due to rotation of the cutter blade, and is received in a container or grass-bag for collecting grass. In the prior art, grass-bag fullness is detected by a sensor provided in the grass-bag, and the worker is informed of that by means of an alarm such as a buzzer.
An example of the conventional, typical detector for detecting the amount of grass in the grass-bag will be described with reference to FIGS. 8A, 8B, 9A and 9B. Grass-bag 11 consists of cover 12 and two container portions, namely, a first bag 11a and a second bag 11b. The grass mown by a cutter blade, not shown, is conveyed within shooter 13 and accumulated in the first and second bags 11a and 11b.
In FIGS. 8A and 8B, a level sensor 28 is provided on the grass-bag in an upper portion, under the discharge opening 13A of shooter 13. The level sensor 28 detects when the height level of the grass accumulated in grass-bag 11 has reached a predetermined value, thereby detecting that the grass-bag 11 is full. Such an apparatus is described, for instance, in the Japanese Kokai Utility Model 63-148125 official gazette.
On the other hand, in the detector shown in FIGS. 9A and 9B, a flow rate sensor 18 is provided in cover 12. Flow rate sensor 18 measures the flow rate of air discharged from grass-bag 11, and the amount of the grass accumulated in grass-bag 11 is determined by the measured air flow rate. Such an apparatus is described, for instance, in the Japanese Kokai Patent 63-24814 official gazette.
The above prior art had the following problems. Since mown grass does not evenly accumulates in the first and second bags 11a and 11b of the grass-bag 11, it is very difficult to accurately detect that the grass-bag is full of mown grass, by use of such sensors 18 and 28.
For instance, if the grass to be mown is wet or its length to be cut is long, the mown grass tends to be first accumulated in the first bag 11a as shown by the shaded portions in FIGS. 8A and 8B. When the method of judging fullness of the bag 11 detects the height level of the accumulated grass, there is a tendency for only first bag 11a to become full before second bag 11b is full, so that fullness of grass-bag 11 may be detected in error (FIG. 8A). Also, when the method of detecting fullness relies on air flow rate, the exit 13A of shooter 13 may jam before second bag 11b becomes full, and furthermore, even fullness detection for preventing a jam cannot be performed (FIG. 9A).
To the contrary, if the grass is dry and sparse, the second bag 11b tends to be accumulated first (FIGS. 8B, 9B). For this, in the method of judging fullness by the height level of the grass, the grass may excessively accumulate and fullness may be detected after the grass begins to jam in the shooter exit 13A (FIG. 8B). On the other hand, in the method of detecting fullness by air flow rate, grass-bag 11 may be misjudged to be full, because the amount of the discharged air decreases before first bag 11a becomes full (FIG. 9B).
If shooter exit 13A has jammed or the grass has excessively accumulated in grass-bag 11, the post-treatment for cleaning of shooter 13 or removal of the grass becomes cumbersome. In addition, if the timing of fullness judgment is too early, more frequent disposal work is needed, which makes the moving operation inefficient.
In order to avoid such inconveniences, the detection sensitivity and set position of the sensor must be adjusted according to the degree of dry or wet, length of the grass to be mown or the work condition. However, it is impossible in fact to optimally perform such adjustment according to the properties of the grass to be mown.